Methods for processing multifunctional, radiation tolerant nanotube-polymer structure composites

ABSTRACT

Embodiments provide a composite material with oriented nanotubes and a method for making the composite material. The composite material can be formed by distributing a plurality of nanotubes in a polymer matrix. The nanotubes can be further magnetically oriented during the formation of the polymeric matrix, while the polymer matrix is magnetically annealed. The composite material can provide enhanced mechanical and electrical properties, and effective radiation resistance against high-energy ionizing radiation particles and/or electromagnetic interferences. The composite material can be useful for lightweight armors incorporated into vehicles, aircrafts or personnel protection with high ballistic properties, and efficient dissipation of radiation energies, photovoltaic cells with improved polymer solar cell efficiency, improved light emitting diodes (LEDs) with controllable optical properties, or infrared screening devices with increased extinction coefficient.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplications Ser. No. 60/711,678, filed Aug. 29, 2005, and Ser. No.60/726,652, filed Oct. 17, 2005, which are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

This invention relates generally to composite materials and, moreparticularly, to composite materials with magnetically orientednanotubes in a polymer matrix.

BACKGROUND OF THE INVENTIONS

Organic materials such as polymers offer an attractive route for a widevariety of applications, such as armor devices, photovoltaic devices,light emitting diodes (LEDs), or infrared screening devices, due totheir advantages of lightweight (i.e. mass-effective), low cost, ease offabrication, and flexibility. For example, polymers used as protectivearmor materials against low-level of threats (e.g., NIJ level III orlower) offer the distinctive advantage of lower density over materialssuch as metals or ceramics. However, because of their relatively lowstrength and hardness, polymers are commonly reinforced with eitherorganic or ceramic fibers/whiskers, and are used in conjunction withharder metals and ceramics when they are used in protective systemsagainst higher level of threats, such as NIJ Level IV or higher. Anexample is standard body armor where a ceramic armor plate is combinedwith Kevlar™ (a type of polymeric synthetic fiber from DuPont Company(Wilmington, Del.)) and graphite fiber in a polyurethane and urea matrixto provide sufficient protection. In another example, polymers may beused as infrared screening films since conventional armor materials suchas metal alloy brass are highly toxic. However, problems arise due tothe low electrical conductivity for most polymers.

Carbon nanotubes possess exceptional mechanical properties and superiorelectric and thermal properties and can be used as reinforcement fibersfor structural composites. For example, a cast composite film consistingof polystyrene and randomly oriented carbon nanotubes (5% volumefraction) has been shown to increase the specific modulus by 100% andthe strength of the polystyrene by 25%. In addition, carbon nanotubereinforcement can increase the toughness of the composite by absorbingenergy because of its high elastic behavior during loading. Furthermore,carbon nanotubes are environmental friendly compared with materials suchas brass in conventional infrared screening devices.

Therefore, it is desirable to combine carbon nanotubes with polymers toprovide distinctive properties. Limitations arise, however, becauseutilizing the unique properties of carbon nanotubes depends on thespatial control and dispersion of individual nanotubes in the polymermatrix, and on the interaction between the polymer and the nanotubes,such as, the ability to transfer load from the matrix to the nanotubes.

Thus, there is a need to overcome these and other problems of the priorart and to provide a controlled processing of nanotubes with polymermatrix forming a composite material with oriented nanotubes.

SUMMARY OF THE INVENTION

According to various embodiments, the present teachings include acomposite material with magnetically oriented nanotubes. To form thecomposite material, a plurality of nanotubes are distributed in one of aresin and a hardener to form a first mixture. A second mixture is thenformed by combining the other of the resin and the hardener with thefirst mixture. The second mixture is then degassed and cured under amagnetic field of about 15 Tesla or more to orient the nanatubes.

According to various embodiments, the present teachings further includea composite material including a polymer matrix with distributednanotubes. The polymer matrix includes at least one of thermosettingpolymers or thermoplastic polymers. The nanotubes are magneticallyaligned during formation of the polymeric matrix.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram of an exemplary method for making a compositematerial in accordance with the present teachings.

FIG. 2 is a schematic diagram for an exemplary magnetically alignedcomposite material 200 in accordance with the present teachings.

FIG. 3 depicts an exemplary armor device 300 providing protection fromprojectile threats in accordance with the present teachings.

FIG. 4 depicts an exemplary method for resisting ionizing radiationswith composite armor material in accordance with the present teachings.

DESCRIPTION OF THE EMBODIMENTS

Embodiments provide a composite material including oriented nanotubesand a method for making the composite material. The composite materialmay be formed by distributing a plurality of nanotubes in a polymermatrix. The nanotubes may be further magnetically oriented during curingof the polymeric matrix. The composite material may provide enhancedmechanical and electrical properties, and effective radiation resistanceagainst high-energy ionizing radiation particles and/or electromagneticinterferences. The composite material can be useful for manyapplications including, but not limited to, armors for vehicles,aircrafts and personnel protection, with high ballistic properties, andefficient dissipation of radiation energies, photovoltaic devices withimproved polymer solar cell efficiency, improved LEDs with controllableoptical properties, and infrared screening devices with increasedextinction coefficient.

Reference will now be made in detail to exemplary embodiments of theinvention, an example of which is illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific exemplary embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention and it is tobe understood that other embodiments may be utilized and that changesmay be made without departing from the scope of the invention. Thefollowing description is, therefore, merely exemplary.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations; the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein. For example, a range of “less than 10” can include any and allsub-ranges between (and including) the minimum value of zero and themaximum value of 10, that is, any and all sub-ranges having a minimumvalue of equal to or greater than zero and a maximum value of equal toor less than 10, e.g., 1 to 5.

As used herein, the term “nanotube” refers to any cylindrical shapedmaterial (including organic or inorganic material) with a diameter ofabout 100 nanometers or less. The term “nanotubes” also refers to singlewall nanotubes, multiwall nanotubes, and their various functionalizedand derivatized fibril forms, which include nanofibers. The nanofiberscan be fibrils with diameters of 100 nm or less in at least one form ofthread, yarn, fabrics, etc.

FIG. 1 shows a block diagram of an exemplary method for forming acomposite material in accordance with the present teachings. It shouldbe readily obvious to one of ordinary skill in the art that the methoddepicted in FIG. 1 represents a generalized schematic illustration andthat other steps may be added or existing steps may be removed ormodified.

As shown in FIG. 1, at 110, a plurality of nanotubes may be provided. Invarious embodiments, the provided nanotubes may be carbon nanotubes,which may include but are not limited to single wall carbon nanotubes(SWCNs) or multi-wall carbon nanotubes. In some embodiments, the SWCNsmay be armchair type nanotubes (n,n).

In various embodiments, the nanotubes may be obtained in low and highpurity dried paper forms or may be purchased in various solutions. Thenanotubes may also be available in the as-processed, unpurifiedcondition, which may carry with them numerous unwanted impurities thatmay affect composite properties. Accordingly, at 110, the plurality ofnanotubes may be provided from a purification process, which utilizesultrasonically assisted filtrations. The ultrasonic energy source maybe, for example, a high-intensity ultrasonic processor. In thepurification process, for example, the nanotubes can be ultrasonicallysuspended in a first solvent, such as, toluene, and then filtered toextract the soluble fullerenes leaving an insoluble fraction. Theinsoluble fraction may then be ultrasonically re-suspended in a secondsolvent, such as a methanol, and transferred in a filtration funnelconfigured with a filter membrane. A pressure differential of, forexample, about 50 Torr, may be applied across the filter membrane. Thefilter membrane may be, for example, a polycarbonate track-etched filtermembrane with a pore size of about 0.8 μm. The obtained nanotubes maythen be washed with a third solvent, such as a sulfuric acid with anexemplary concentration of 6 M, to remove traces of metal such astitanium introduced into the sample from the ultrasonic horn.

At 120 of FIG. 1, a plurality of nanotubes can be distributed in aresin. Distributing nanotubes in a resin may further include firstdispersing nanotubes in a solvent, such as an ethanol, and thenultrasonically mixing nanotube-ethanol, for example, at about 10%amplitude for about 90 seconds using the high-intensity ultrasonicprocessor. Meanwhile, the resin may also be ultrasonically mixed withethanol at about 10% amplitude for about 90 seconds. Thenanotubes/ethanol mixture may then be combined with the resin/ethanolmixture and ultrasonically mixed at about 50% amplitude for about 90seconds. This process may promote the distribution of nanotubes over thesurface of the resin molecules and prevent nanotube clustering. Theexemplary embodiment described herein utilizes a polymer matrix formedof DERAKANE 411-350 epoxy vinyl ester resin manufactured by Ashland Inc.(Covington, Ky.).

Still at 120 of FIG. 1, to form the composite material, a designatedweight fraction of purified nanotubes, such as, for example, 35% or lessby weight, may be dispersed in a hardener part of an epoxy by firstdispersing the plurality of nanotubes in a solvent such as ethanol in anultrasonic bath at room temperature for about one hour. Then theethanol-based nanotube solution may be mixed with the hardener and themixture may be stirred for at least one hour at about 2000 rpm or more.During this stirring process, the nanotube-hardener mixture may be keptat room temperature to maintain a low viscosity using a silicon oil bathfor example. In various embodiments, the solvent ethanol may be removedby evaporation where the mixtures may be placed in a vacuum oven atabout 60° C. or more for at least one hour.

At 130 of FIG. 1, a resin part of the epoxy may then be added to thenanotube-hardener mixture to form a composite mixture with a desiredresin/hardener ratio, such as 4:1 by weight. The epoxy may include, butare not limited to, one or more of aeropoxy, thixotropic epoxy,Derakane-441, or other type of epoxy. The composite mixture may bestirred at about 2000 rpm or more for at least 5 minutes.

At 140 of FIG. 1, the composite mixture may be degassed moderately untilno gas bubbles can be seen. The degassed mixture may then be loaded intomolds of a desired shape which may result in a variety of 3-D structuresfor the nanotube-polymer composite, such as, for example, a sheet, afiber, a cylinder, a foam or other 3-D structure. The molds may besealed for a subsequent magnetic process. In various embodiments, thedegassed composite mixture may be formulated as a film or coated onvarious substrates and then be loaded for a subsequent magnetic process.

At 150 of FIG. 1, the composite mixture may be cured at room temperaturewith a low viscosity under a high magnetic field, such as 15 Tesla ormore for at least 2 hours. Then, still under the high magnetic field,the curing temperature may be increased up to about 60° C. or more foralso at least 2 hours. During the magnetic process, the polymer may beannealed and the nanotubes may be oriented in the polymer matrix (i.e.the curing mixture of the resin and the hardener of the epoxy in thisexample) due to the cooperative effect of the magnetic torque exerted bythe magnetic field directly on the nanotubes and by hydrodynamic torqueand viscous shear (i.e. drag forces) exerted on the nanotubes by thepolymer chains. In addition, the magnetic field may be penetrable andits direction and strength may be controllable. Accordingly, thealignment of the nanotubes may be controlled for desired orientation(s)depending on specific applications. More specifically, the alignmentprofile may be specially designed for desired enhanced properties of thecomposite material, such as enhanced mechanical and electricalproperties, or efficient radiation resistance.

Turning to 150 of FIG.1, the magnetic field may then be removed and thecomposite mixture may remain cured at about 60° C. or more for at least2 hours to fully cure the polymer matrix, i.e., the resin and thehardener of the epoxy in this example. One of ordinary skill in the artwill understand that other polymers may be also used for the polymermatrix including but not limited to thermosetting polymers andthermoplastic polymers. In various embodiments, boron carbide particles,silicon carbide particles, or other similar hard materials may beincorporated into the polymer matrix for the composite material.

FIG. 2 shows a schematic diagram of an exemplary magnetically orientedcomposite material 200 including a plurality of nanotubes 210 andpolymer fibrils 220 formed in accordance with the present teachings.Arrow 230 indicates a direction of the applied magnetic field. It shouldbe readily obvious to one of ordinary skill in the art that theexemplary magnetically oriented composite material 200 depicted in FIG.2 represents a generalized schematic illustration and that morenanotubes or polymer fibrils may be added or existing nanotubes orpolymer fibrils may be removed or modified.

As shown in FIG. 2, the plurality of nanotubes 210 can be oriented in adirection parallel to the magnetic field indicated by the arrow 230. Insome embodiments, the nanotubes 210 may be magnetically oriented singlewall carbon nanotubes (SWCNs). In other embodiments, the nanotubes 210may be locally oriented, for example, through a mechanical stretching,or a pressing through a die or electric field. As a result, thecomposite material 200 with locally oriented nanotubes may providespecially-varying mechanical properties for specific applications, suchas, for example, a composite tube with strong exterior and softinterior.

The polymer fibrils 220 may be uniform along the direction of themagnetic field indicated by the arrow 230. When a magnetic field isapplied during the formation of the polymer, such as, for example,during the curing of a liquid epoxy, the polymer molecules may also beannealed (e.g., aligned) along the direction of the applied magneticfield and taking fibril shape. Accordingly, the polymer fibrils 210 maybe magnetically aligned epoxy fibrils in accordance with variousembodiments.

In various embodiments, the magnetically oriented composite material 200may provide enhanced mechanical and electrical properties. The enhancedmechanical properties may be demonstrated by a specific strength and aspecific modulus. The specific strength (or modulus) may be determinedby a material strength (or modulus) divided by its density (e.g;, weightper unit volume). For example, the magnetically oriented compositematerial 200 may provide a specific strength of such as about 20GPa·cm²/g to about 50 GPa·cm²/g and a specific modulus of such as about100 GPa·cm²/g to about 200 GPa·cm²/g.

The enhanced electrical properties for the magnetically orientedcomposite material 200 may be demonstrated by the electricalconductivity, such as, for example, an electrical conductivity of about10⁶ s·cm⁻¹ or higher. Because of this enhanced electrical conductivity,the magnetically oriented nanotube-polymer composite material 200 may beused for, for example, improved polymer-based light emitting diodes(LEDs), especially when the polymer used is a photo-active polymer.Compared with conventional LEDs, the nonotube-polymer based compositematerial may be able to increase photoluminescence/electro-luminescenceyield, which may provide a means to alter the optical properties of thepolymer to tune the color or emission for organic light emittingdevices. One more example for using the enhanced electrical conductivityof the magnetically oriented nanotube-polymer composite material 200 maybe for infrared screening devices. The magnetically oriented compositematerial 200 may be used as an environmental friendly alternative toscreen infrared radiations compared to highly toxic materials that isconventionally in use such as brass. More importantly, the enhancedelectrical conductivity of the magnetically oriented composite material200 may increase the extinction coefficient for infrared screening.

Accordingly, the magnetically oriented composite material 200 withenhanced mechanical and electrical properties may be used for ballisticresistant material such as armor devices, that may be as effective assteel against projectiles—at considerably lower weight. FIG. 3 shows anillustration for an armor device 300 that may provide protection frompossible projectile threats in an application of such as a ground combatvehicle. It should be readily obvious to one of ordinary skill in theart that the armor device 300 depicted in FIG. 3 represents ageneralized schematic illustration and that other layers may be added orexisting layers may be removed or modified.

In the armor device 300, the magnetically oriented composite material200 may be configured as armor interior 350. The armor interior 350 maybe overlaid by a layer 352 of metal, such as aluminum, then a layer 354of ceramic, such as alumina (i.e., aluminum oxide), and then a layer 356of metal, such as steel. The layer 352, 354, and 356 may be configuredas an armor cover over the armor interior 350.

To form the armor interior 350, the magnetically oriented compositematerial 200 may undergo a scale up fabrication process to meet specificapplications. Accordingly, the resulting armor interior 350 may be atleast one form of films, sheets, fibers, cylinders, foams, coatings orpastes.

As used for the armor interior 350, the nanotubes may be magneticallyoriented in certain directions with a high anisotropy due to itsone-dimensional structure. Such magnetic orientation of nanotubes(including nanofibers) may be controlled to confer specific propertiesto the armor interior 350. For example, by rearranging the orientationsof nanotubes, superior mechanical and physical properties may betailored to the armor interior 350. In some embodiments, the orientednanotubes in the armor interior 350 may be aligned co-axially with theline of fire to provide shear load transfer in the frontal impact layer.In other embodiments, the oriented nanotubes in the armor interior 350may be aligned orthogonally to the line of fire to provide tensile loadsupport in the structural baking layer.

In various embodiments, the magnetically oriented composite material 200may further be used as a shielding material and provide effectiveradiation resistance against high-energy ionizing radiation particlesand/or electromagnetic interferences in applications such as armordevices.

FIG. 4 depicts a method for resisting radiation including a radiationsource 410 and an armor device 420. The armor device 420 may include acomposite armor material 430 enclosed in an armor enclosure 440 formedwith materials, such as aluminum. The composite armor material 430 mayinclude the magnetically oriented composite material 200.

The radiation source 410 may provide ionizing particles, electromagneticinterferences, or a combination of various radiations. The ionizingparticles may include alpha particles, beta particles, gamma rays or xrays, cosmic ray or solar flares. To measure the radiation resistance,the radiation source 410 may provide radiations with high energy, suchas, for example, an ionizing particle with a proton beam for a radiationenergy of 15 MeV (i.e. megaelectron volts) or higher. Alternatively, theradiation source 410 may provide a proton beam with high intensities,such as, ranging from the direct level of 109 beam particles per secondto 10 beam particles per second. Such high energy radiation may be farmore intense than would be expected in a real environment, such as inspace.

The armor device 420 may be exposed to the radiation source 410 tomeasure the radiation resistance of the composite armor material 430.The radiation resistance may be demonstrated by a shieldingeffectiveness (or attenuation fraction) that may be measured. Forexample, when using a high-energy proton beam as radiation source 410,the shielding effectiveness (or attenuation fraction) may be measured interms of the number of high-energy particles in the beam before andafter the proton beam hits the shielding material, i.e. the magneticallyoriented composite armor material 430. The shielding effectiveness orattenuation fraction for the composite armor material 430 may be, forexample, about 0.60 or higher. In some embodiments, the composite armormaterial 430 may include magnetically aligned nanotubes with high aspectratio for providing enhanced transport properties for effectiveelectromagnetic interference shielding for electronics, which in somecases may also need to be guarded against impact damages.

Generally, armor devices, such as, for example, the armor device 300 inFIG. 3 or the armor device 420 in FIG. 4, may be incorporated withinvehicles, aircrafts or personnel armors to provide lightweightprotection against ballistic threats, enhanced mechanical and electricalproperties, and radiation protection against high-energy ionizingparticles and/or electromagnetic interferences.

In various embodiments, the magnetically oriented composite material 200may also provide electronic properties based on morphologicalmodification or electronic interaction between the two components, suchas, for example, π-conjugated polymers and carbon nanotubes. Inparticular, the combination of carbon nanotubes with π-conjugatedpolymers may form an electronic conjugation which may enable thepolymers to be used as an active material for photovoltaic devices, suchas a photovoltaic cell. The controlled magnetic processing of carbonnanotubes with π-conjugated polymers may improve the excitondissociation and carrier transport of the system and thus resulting inan improved polymer solar cell efficiency.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A composite material formed by the steps comprising: providing aplurality of nanotubes; distributing the plurality of nanotubes in oneof a resin and a hardener to form a first mixture; forming a secondmixture by combining the other of the resin and the hardener with thefirst mixture; degassing the second mixture; and curing the secondmixture under a magnetic field of about 15 Tesla or more to orient theplurality of nanotubes.
 2. The composite material of claim 1, whereinthe plurality of nanotubes comprise nanofibers.
 3. The compositematerial of claim 1, wherein the plurality of nanotubes comprise carbonnanotubes, wherein the carbon nanotubes comprise one of single wallcarbon nanotubes (SWCNs) or multi-wall carbon nanotubes.
 4. Thecomposite material of claim 3, wherein the SWCNs comprise armchair typenanotubes having a chirality where n=m.
 5. The composite material ofclaim 1, wherein a weight percentage of the plurality of is 35% or lessof the composite material.
 6. The composite material of claim 1, whereinthe resin and the hardener form an epoxy with low viscosity at roomtemperature.
 7. The composite material of claim 1, wherein the pluralityof nanotubes are oriented anisotropically.
 8. A ballistic resistantmaterial comprising the composite material of claim 1, wherein theplurality of nanotubes are aligned co-axially to a line of impact.
 9. Aballistic resistant material comprising the composite material of claim1, wherein the plurality of nanotubes are aligned orthogonally to a lineof fire or a line of impact.
 10. A ballistic resistant materialcomprising the composite material of claim 1 further comprising at leastone of boron carbide and silicon carbide.
 11. The composite material ofclaim 1 further comprising at least one form of a film, sheet, fiber,cylinder, foam, coating or paste.
 12. A method for making a compositematerial comprising: providing a plurality of carbon nanotubes;distributing the plurality of carbon nanotubes in a hardener; forming amixture by combining a resin with the hardener and the plurality ofcarbon nanotubes; degassing the mixture; and curing the mixture under amagnetic field of about 15 Tesla or more to align the plurality ofnanotubes.
 13. The method of claim 12 further comprising: adding a firstsolvent to the plurality of carbon nanotubes, wherein the first solventcomprises an ethanol; adding a second solvent to the resin, wherein thesecond solvent comprises an ethanol; and combining the first solvent andthe plurality of carbon nanotubes with the second solvent and the resin.14. The method of claim 12, wherein providing the plurality of carbonnanotubes comprises purifying the carbon nanotubes.
 15. The method ofclaim 12 further comprising providing a solvent for steps of providingcarbon nanotubes and distributing the carbon nanotubes in the hardener,wherein the solvent comprises an ethanol.
 16. The method of claim 12further comprising placing the carbon nanotubes distributed hardener ina vacuum at about 60° C. or more for at least one hour.
 17. The methodof claim 12 further comprising stirring the mixture at about 2000 rpm ormore for at least 5 minutes prior to the step of curing.
 18. The methodof claim 12, wherein curing the mixture comprises: curing the mixture atroom temperature for at least two hours under the magnetic field; curingthe mixture at about 60° C. or more for at least two hours under themagnetic field; and curing the mixture at about 60° C. or more for atleast two hours under no magnetic field.
 19. A composite materialcomprising: a polymer matrix, wherein the polymer comprises at least oneof a thermosetting polymer and a thermoplastic polymer; and a pluralityof nanotubes distributed in the polymer matrix, wherein the plurality ofnanotubes are magnetically aligned during formation of the polymericmatrix.
 20. A ballistic resistant material comprising the compositematerial of claim 19, wherein the plurality of nanotubes are alignedco-axially to a line of impact.